I don't know what they're called, there a spot with 3 small circles with missing parts and a small'bar'. I pointed at the missing pieces.
There's a name carved on it on the inside. Please know the product before purchasing, know what it is and how to use it. Please see pictures for further details. This item is in the category "Business & Industrial\CNC, Metalworking & Manufacturing\Metalworking Inspection & Measurement\Indicators". The seller is "planetofweirdthings" and is located in this country: US.
This item can be shipped worldwide.